1. Field of the Invention
The present general inventive concept relates to an electrophotographic image forming device, such as a laser printer, a digital photocopier, or a facsimile machine. More particularly, the present general inventive concept relates to a roller spacing apparatus to space apart two rollers (e.g., a photoconductive medium and a developing roller, or a photoconductive medium and a charging roller) that rotate in close contact with each other under a predetermined pressure by a predetermined distance, and to maintain the two rollers in a non-contact state when the two rollers are not in use (e.g., during shipping), and an image forming device having the roller spacing apparatus.
2. Description of the Related Art
Generally, an electrophotographic image forming device, such as a laser printer, a digital photocopier, or a facsimile machine includes a photoconductive medium (e.g., a photoconductive drum) to form a developer image.
A charging roller, a laser scanning unit (LSU), and a developing roller are disposed at predetermined locations around an outer circumference of the photoconductive medium along a rotational direction. The charging roller charges a surface of the photoconductive medium to a predetermined electric potential, the LSU scans the surface of the charged photoconductive medium with laser beams and thereby forms an electrostatic latent image on the surface of the photoconductive medium, and the developing roller supplies a developer to the surface of the photoconductive medium and thereby forms the developer image corresponding to the electrostatic latent image.
The developing roller and the charging roller are rotated in close contact with the photoconductive medium under a predetermined pressure. The photoconductive medium, the developing roller, and/or the charging roller include an elastic layer, such as a rubber layer, to provide protection from a contact damage.
The image forming device maintains the photoconductive medium and the charging roller and/or the developing roller with the elastic layer in close contact until the image forming device is delivered to a user. As a result, the elastic layer is physically and permanently compression set, or is chemically changed to cause high viscosity low molecular organic matter of the elastic layer to come out from a surface of the elastic layer. The high viscosity low molecular organic matter is combined with the developer and adheres to the surface of the photoconductive medium. In this case, physical and chemical changes may cause device components to malfunction and may cause image degradation. As a result, a reliability of the device may deteriorate. In some cases, a deformed roller, or even the image forming device itself, has to be replaced.
The photoconductive medium, the charging roller, and the developing roller are fabricated as a process cartridge that integrates components into a housing as a single module unit, so that the components are easily detachable from a body of the electrophotographic image forming device for easy repair or replacement.
If the process cartridge fabricated for replacement is not in use (e.g., after being purchased by a user, but before being mounted in the body of the image forming device), the photoconductive medium and the charging roller and/or the developing roller are typically in close contact with each other during the period of non-use. Accordingly, there is a problem that the elastic layer of the photoconductive medium, the developing roller, and/or the charging roller may be physically or chemically damaged.
In an effort to address this problem, the image forming device or the process cartridge includes an apparatus for spacing apart the charging roller or the developing roller from the photoconductive medium when not in use (i.e., in the period of non-use).
FIGS. 1 to 3 are views illustrating a conventional roller spacing apparatus 1, which spaces a developing roller 20 from a photoconductive medium 10 when an image forming device is not in use.
Referring to FIGS. 1 to 3, the roller spacing apparatus 1 includes a spacing member 30 disposed at a shaft 21 of a developing roller 20 (i.e., the developing roller shaft 21), and the spacing member 30 is movable between a first position and a second position. As illustrated in FIG. 2, if the spacing member 30 is at the first position (in a contact state), the developing roller 20 is not spaced apart from the photoconductive medium 10. As illustrated in FIG. 3, if the spacing member 30 is at the second position (in a non-contact state), the developing roller 20 is spaced apart from the photoconductive medium 10 by a predetermined gap “g.”
The spacing member 30 includes a spacing protrusion 35 that is brought into contact with a stepped portion 12 of a driving gear 11 of the photoconductive medium 10 when the spacing member 30 is at the second position (FIG. 3), and spaces apart the developing roller 20 from the photoconductive medium 10 by the predetermined gap “g.”
The spacing member 30 is movable between the first and the second positions along the shaft 21 of the developing roller 20 by a spacing member moving part 40.
The spacing member moving part 40 includes a first rotary member 41 and a second rotary member 42. The first rotary member 41 is idly rotatable around the developing roller shaft 21 and the second rotary member 42 is rotatable integrally with the developing roller shaft 21 at a D-cut portion 22 of the developing roller shaft 21. The first and the second rotary members 41 and 42 are restricted by fixing members 48 and 47, respectively, so that the first and the second rotary members 41 and 42 do not move in a lengthwise direction of the developing roller shaft 21.
As illustrated in FIG. 3, the roller spacing apparatus 1 has a rotary knob 50 into which the D-cut portion 22 of the developing roller shaft 21 is inserted to rotate the second rotary member 42. When the developing roller shaft 21 is rotated after being inserted into the rotary knob 50, the developing roller shaft 21 and the second rotary member 42 are rotated in the same direction. The first rotary member 41 is rotated according to a rotational movement of the photoconductive medium 10 when the image forming device operates.
An operation of the conventional roller spacing apparatus 1 will now be described.
The rotary knob 50 is rotated in one direction (i.e., in a counter clockwise direction) after being combined with the shaft 21 of the developing roller 20 of the image forming device or a process cartridge, which has passed a printing test of an image quality test.
As the rotary knob 50 is rotated, the second rotary member 42 and the developing roller shaft 21 are rotated together with the rotary knob 50 in the counter clockwise direction. At this time, a third rotary projection 45 and a fourth rotary projection 46 of the second rotary member 42 are rotated along a second inclination surface 36 of the spacing member 30, thereby moving the spacing member 30 to the second position of the developing roller shaft 21.
As illustrated in FIG. 3, the spacing protrusion 35 of the spacing member 30 is brought into contact with the stepped portion 12 of the driving gear 11 of the photoconductive medium 10 due to the movement of the spacing member 30 such that the developing roller 20 is spaced apart from the photoconductive medium 10 by a distance that can be as much as a height of the spacing protrusion 35.
Accordingly, the conventional roller spacing apparatus 1 is intended to space the developing roller 20 form the photoconductive medium 10 when the image forming device or the process cartridge is placed on the market. The developing roller 20 and the photoconductive medium 10 are intended to remain spaced apart from one another until the image forming device or the process cartridge is delivered to a user.
When the image forming device or the process cartridge performs a printing operation, the first rotary member 41 is rotated in the counter clockwise direction by a driving force transmitted from a main driving device of the image forming device to the first rotary member 41 through the driving gear 11 of the photoconductive medium 10. At this time, a first rotary projection 43, which is lockable into a first locking portion 31 of the spacing member 30, and a second rotary projection 44, which is lockable into a second locking portion 32 of the spacing member 30, are rotated along a first inclination surface 37 of the spacing member 30, thereby moving the spacing member 30 from the second position of the developing roller shaft 21 to the first position (i.e., the contact state).
This occurs when the spacing protrusion 35 is removed from the stepped portion 12 of the driving gear 11 of the photoconductive medium 10 by the movement of the spacing member 30, and as a result, the developing roller 20 is brought into contact with the photoconductive medium 10.
During this process, the second rotary member 42 and the developing roller 20 are not initially rotated because the third and the fourth rotary projections 45 and 46 of the second rotary member 42 are not locked into a third locking portion 33 and a fourth locking portion 34, respectively, until the spacing member 30 is rotated by 180°.
Once the developing roller 20 is moved into the contact state of the first position, when the first rotary member 41 is rotated at least one time, the spacing member 30 is rotated by more than 1800. Accordingly, the third and the fourth rotary projections 45 and 46 of the second rotary member 42 are respectively locked into the third and the fourth locking projections 33 and 34 of the spacing member 30. As a result, the rotational force of the first rotary member 41 is transmitted to the second rotary member 42, and the developing roller 20 is rotated along with the second rotary member 42 in the counter clockwise direction. That is, the photoconductive medium 10 and the developing roller 20 are rotated in close contact with each other and perform a developing operation.
As illustrated in FIG. 2, when the main driving device of the image forming device stops performing a driving operation, the first and the second rotary projections 43 and 44 of the first rotary member 41, the third and the fourth rotary projections 45 and 46 of the second rotary member 42, and the spacing protrusion 35 of the spacing member 30 that interact with the aforementioned corresponding elements, maintain the contact state as long as the user does not forcibly-rotate the shaft 21 of the developing roller 20 by using the rotary knob 50.
However, the conventional roller spacing apparatus 1 has the spacing member 30 and the first and the second rotary members 41 and 42 located at a first end portion of the shaft 21 of the developing roller 20 to space out the developing roller 20 from the photoconductive medium 10.
Accordingly, in operation, only the first end portion of the developing roller 20 is spaced away from the photoconductive medium 10 by a distance of as much as the height of the spacing protrusion 35. However, a second end portion of the developing roller 20 opposite from the first end portion is not spaced apart from the photoconductive medium 10 by a distance of as much as the height of the spacing protrusion 35, and the second end portion of the developing roller 20 remains in the contact state with the photoconductive medium 10. As a result, an elastic layer formed on the second end portion of the developing roller 20 or on a corresponding portion of the photoconductive medium 10 is physically and permanently compression set. Otherwise, high viscosity low molecular organic matter that comes out of the elastic layer of the developing roller 20 or the photoconductive medium 10 is combined with a developer, and thus is fixed to a surface of the developing roller 20 and/or the photoconductive medium 10.
Since the conventional roller spacing apparatus 1 has no element to guide or restrict the movement of the spacing protrusion 35, which spaces out the developing roller 20 from the photoconductive medium 10, it is difficult to set the spacing protrusion 35 of the spacing member 30 above the driving gear 11 of the photoconductive medium 10. Also, when the image forming device or the process cartridge is delivered, the spacing protrusion 35 changes position, and thus a motion stability of the spacing member 30 cannot be obtained. In other words, the spacing member 30 does not remain in a predetermined position when the roller spacing apparatus 1 is moved.